Recently, navigation systems for displaying a current vehicle position on a map have been widely adopted in vehicles. A typical navigation system calculates the current vehicle position on the basis of a GPS (Global Positioning System) signal received from a GPS satellite, and displays the calculated vehicle position on a display device.
A complication is introduced in navigation because vehicles not only run on simple roads formed on land, but also run on roads having a plurality of road layers (referred to as “multi-layer road” in the whole specification) such as an overpass or flyover. In the case that a vehicle is running on an upper road or lower road of a multi-layer road, typical navigation systems do not precisely determine whether the vehicle is running on the upper road or on the lower road, such that sometimes guiding of the vehicle route becomes erroneous.
For example, in the case that a vehicle is running on an upper road of a multi-layer road where there is no exit or crossway, the navigation system may display guiding instructions of “left turn” or “right turn” because the navigation system may incorrectly determine that the vehicle is running on the lower road where such exit or crossway exists. This kind of malfunctioning of a navigation system has been proven to be more frequent in the case in which the navigation system commences operation when the vehicle is running on the multi-layer road.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art that is already known to a person skilled in the art.